Draft. Compliance criterion Detached houses Attached houses Low rise apartment blocks. Equiv. improvement over 2006 Part L 60% 56% 44%

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1 Carbon Compliance: A study comparing PHPP and SAP calculations of C0 2 emissions for three of the first Certified Passivhaus dwellings in the UK, to test theoretical correlation with the UK Government s 2011 definition of Zero Carbon. Nick Newman bere:architects June SAP calculations and consultancy by Brooks Devlin Ltd. 1.0 Introduction With much attention focused at the time of writing on the UK government s decision on the 2016 definition of Zero Carbon, the construction industry now needs to focus on the precise steps that need to be taken towards achieving these targets. There will be particular interest in finding the most cost effective and reliable design methodologies. Developers will be responsible for actual fabric performance, so performance reliability will be a key factor in their choice. The conclusions of this report analyse how closely in practice a certified passivhaus and a Spec D house perform; indicate the most cost effective solutions to achieving compliance (although this is covered seperately in three other reports by bere:architects, now nearing completion); and indicate that at statutory level, it would be sensible, in the interests of efficiency and industry, to accept Passivhaus as an alternative method of meeting and exceeding the future regulatory criteria for low energy design. 1.1 Premise of this report This report aims to investigate the performance of three Certified Passivhaus dwellings in the UK, and through the use of established energy modelling software, compare and contrast these performance outputs with equivalent targets within the 2016 Zero Carbon definition. It is hoped that this exercise will help to inform discussion as to the suitability of Passivhaus dwellings for meeting the UK s low energy building requirements, and potentially stimulate further investigation into this field of research. 1.2 Background On 18 th May 2011, housing minister Grant Shapps reaffirmed the UK government s commitment to the future delivery of low energy housing, by issuing a formal decision on the definition of Zero Carbon 1. Although some technical details are subject to further consultation, the statement highlights the government s broad intention to follow the recommendations of the Zero Carbon Hub (ZCH) report Carbon Compliance Findings and Recommendations 2, published in Feb The decision puts the government on a path towards fulfilling current European Directive 2010/31/EU, which instructs that Member States shall ensure that by 31 December 2020, all new buildings are nearly zero energy buildings 3 As a result of the decision, developers of housing from 2016 will be required to account for the regulated emissions, or those which eminate from the functioning of the building itself, eg. space heating, building services etc. They will not be accountable for the in use emissions of unregulated loads, such as appliances and small electronics. Buildings which conform to this policy will be referred to as Carbon Compliant. 1.3 Carbon Compliance The Carbon Compliance recommendation as endorsed by the 18 th May decision comprises a minimum building fabric energy efficiency standard of 39 to 46kWh/m 2 a dependent on house type and a further allocation of on site low or zero carbon (LZC) technology. Carbon Compliance equates to approximately 44 60% over the 2006 standard depending on house type, with the requirement that remaining emissions are negated through offsite allowable solutions. The Government has proposed the adoption of three absolute Dwelling Emission Rate limits (DER) in order to demonstrate 2016 Carbon Compliance. (see Figure i below). Compliance criterion Detached houses Attached houses Low rise apartment blocks Dwelling Emission Rate (DER) 10 kg CO 2 (eq)/m2a 11 kg CO 2 (eq)/m2a 14 kg CO 2 (eq)/m2a Equiv. over 2006 Part L 60% 56% 44% Figure i: Carbon compliance targets for different building types, summarised from the ZCH 2016 Carbon Compliance report, FEES The Fabric Energy Efficiency Standard (FEES) recommendation for a Specific Energy Demand of 39 to 46kWh/m 2 a was based on a comparative study of a selection of design performance specfications, ranging from current building practice through to EST Advanced Practice, and finally the exacting Passivhaus Standard. The modelling of these performance specifications was carried out using the UK government s Standard Assessment Procedure (SAP), with the passivhaus equivalent SPEC D house influenced by some 1 Communities and Local Government Buildings and the Environment Written ministerial statement 17 th May Accessed June 2011 at 2 Zero Carbon Hub (2011) Carbon Compliance Findings and Recommendations. Accessed May 2011 at 3 Council Directive (EC) DIRECTIVE 2010/31/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 19 May 2010 on the energy performance of buildings (recast) 4 Zero Carbon Hub (2009) Defining a fabric energy efficiency standard for Zero Carbon Homes. Page 7. Accessed May 2011 at

2 additional modelling using the Passivhaus Planning Package (PHPP) 2. The final outputs for the report were based on a modified version of SAP 2009, with the carbon emissions factors altered as per Figure ii to reflect the theorised carbon intensity of the 2016 energy grid. Fuel source SAP 2005 SAP 2009 ZCH 2016 PHPP 2007 Grid electricity Mains gas Figure ii: Comparing carbon emission factors from the ZCH 2016 report with recent SAP and PHPP methodology. Although a thorough discussion of the carbon intensity figures is clearly beyond the scope of this report, it is of key importance to note that the highest values for each fuel type are those found in the PHPP model. As all certified Passivhaus dwellings are assessed independently using PHPP, this can be seen to have the effect of ensuring inherently conservative estimates for Passivhaus performance in the UK. It is also interesting to note the increasing carbon intensity factors for the successive SAP based calculations. If these are to represent a true picture of the UK energy grid in 2016, an increasing burden will be placed on the UK government to provide alternative solutions for those building emissions not negated through building fabric s. 2.0 Initial investigations 2.1 Relationship of Carbon Compliance and FEES The Carbon Compliance and FEES definitions are of great relevance to the findings of this report, so it is of key importance to ensure that the relationship between these two targets is fully established (see below). Figure iii: From ZCH Report, Energy demand of different detached house specifications Figure iii is taken from the ZCH 2009 Defining a Fabric Energy Efficiency Standard, Appendix A Work Group 1 Form and Fabric. It is one of a number of charts showing the regulated energy demand figures (kwh/m 2 a) of each of the chosen building performance specifications which were modelled in the report. As discussed in section 3.0, these specifications range from current practice (Baseline) to a Passivhaus equivalent (SPEC D MVHR) and in this table are also broken down into each of the regulated emissions: Space heating, Hot water, Pumps & fans, Lighting. Whilst there is much that can be read from Figure iii, the chart does not make any easily identifiable reference to the Carbon Compliance/DER metric of kg C0 2 /m 2 a, which therefore makes it difficult to compare FEES performance specifications with the DER targets. Figure iv, taken from the ZCH 2011 Carbon Compliance, Setting an appropriate limit for zero carbon new homes, Findings and Recommendations, is often referred to as a method for clarifying the three steps to net Zero Carbon emissions. Figure iv: From ZCH Report, Diagram showing relationship of FEES, LZC and Allowable Solutions Whilst this is a useful diagram for explaining the Zero Carbon concept, it is not repeated with any target figures or reductions.

3 Figure v combines elements of the two previous diagrams to establish a clearer correlation between the two targets. The results have been by converting each of the specific energy demand figures from Figure iii (kwh/m 2 a) into DER equivalents (kg C0 2 /m 2 a), using the ZCH 2016 carbon intensity factors highlighted in Figure ii. See Appendix A. Figure v: Comparing DER and FEES requirements for detached houses (input data from ZCH 2016 report) 2.2 Initial findings The first main point to note from Figure v is that, based on these calculations, for a Detached house at least it will only be possible to achieve the 2016 FEES limit with an MVHR ventilated SPEC C or SPEC D building. 2.3 PHPP and SAP At the time of writing, the disparity in approach and output of these energy modelling protocols is a topic of widespread discussion. The following excerpts from the 2008 AECB study A comparison of PHPP with SAP 5 give a degree of insight into some of the current debate around this issue.7.2 SAP and PHPP use the same basic principles steady state heat loss multiplied by degree days, with internal and solar gains subtracted. However, we find when comparing models of well insulated houses that the results are very different......overall, SAP plays down the significance of insulation and airtightness, and assumes high levels of internal gains, leading designers to believe they have reached a sensible lower limit on heat loss when in fact they have not......the estimation of CO2 emissions in SAP is significantly lower than in PHPP, even allowing for differences between the electricity systems in the UK and Germany. The AECB study established key disparities between the approaches and suggested possible methods for normalising SAP and PHPP outputs; indeed there is a good deal of research being carried out currently in this 5 Clarke et al. (2008) Projecting Energy Use and Co2 Emissions from Low Energy Building:, A Comparison of the Passivhaus Planning Package (PHPP) and SAP. Accessed May 2011 at An additional point is that the DER of both the SPEC C MVHR (13.0 kg C0 2 /m 2 a) and the SPEC D passivhaus (10.9 kg C0 2 /m 2 a) are above the limit of 10.0 kg C0 2 /m 2 a for a detached house and will therefore require some form of on site LZC technology. In order to carry out any further analysis of these initial findings towards the report aim, it becomes necessary to contrast the conclusions of the report with the certifed design performances for each of the Certified Passivhaus dwellings. One of the selection criteria for the projects were that they had all been modelled using both PHPP and SAP for Passivhaus Certification and Building Regulations respectively. With data available from two sources, it is hoped that an interesting cross reference can be made with the Zero Carbon hub findings. However before this can happen, it is first necessary to discuss the existing connection between PHPP and SAP.

4 field. It is therefore not the aim of this exercise to interpret underlying differences between these two energymodelling procedures. It will however be necessary to make certain straightforward adjustments to both of the SAP and PHPP procedures in order to allow both to be compared more directly with the findings of the 2016 ZCH report (see Method for Comparison below). Any remaining disparity between the outcomes of the two methodologies will then form a basis for further investigation and discussion. 3.0 Method 3.1 Steps for comparison i) For each of the sample buildings, copies of the final PHPP and SAP certification worksheets will be obtained. ii) The differences in carbon intensity highlighted in Figure ii will be normalised for each of the PHPP and SAP worksheets, so that they correlate with the ZCH calculations. iii) Any calcultion input relating to unregulated emissions will be negated. iv) All C0 2 outputs from PHPP and SAP will be compared with the Compliance criteria highlighted in Figure i. v) The impact of PHPP regional variation will be investigated by adjusting all PHPP climate data input to the BRE regional data set for East Pennines considered as the base average weather region in the ZCH report. vi) An equivalent Part L 2006 compliant building will be modelled in PHPP and normalised as per steps i) iii). The C0 2 emission output from this PHPP worksheet will be used as an equivalent Part L Target vzemission Rate, to which all PHPP output then be compared 3.2 Data input for study All data for the study will be based on three of the UK s first passivhaus dwellings, designed by bere:architects in collaboration with Alan Clarke, Warm Associates, Brooks Devlin, the BRE, et al. The projects were certified by BRE Wales (Larch and Lime house) and Warm Associates (Camden Passivhaus) between April 2010 and March The details for each of the projects are set out below: Larch House Lime House Camden Passivhaus Located in Ebbw Vale, Wales Located in Ebbw Vale, Wales Located in North London, England Exposed heads of valley location Exposed heads of valley location Moderately sheltered urban location Space heating demand of 13 kwh/m 2 a Space heating demand of 17 kwh/m 2 a Space heating demand of 13 kwh/m 2 a Primary energy demand of 83 kwh/m 2 a Primary energy demand of 87 kwh/m 2 a Primary energy demand of 97 kwh/m 2 a Detached 3 bedroom house (social) Detached 2 bedroom house (social) Detached 2 bedroom house (private) 4.7kWp PV array, flat panel collectors 2.5kWp PV array, flat panel collectors 3m 2 evacuated tube solar collectors Figure vi: Table comparing key details for the three sample buildings, all certified to the Passivhaus standard. Note: The lime house was certified with a peak heat load figure of 10W/m 2 instead of the more conventional space heating demand certification method. More to be added here...

5 3.3 Modelling assumptions SAP only alterations All three projects were originally certified using SAP For this report they have been recalculated using SAP 2009, as per the ZCH technical modelling assumptions 5 PHPP & SAP alterations 3.4 Step by step adjustments All three projects have some form of LZC technology installed on their roofs. These have been removed from the calculations, in order to focus attention solely on fabric performance. The default carbon emission factors for mains gas and grid electricity have been replaced with the equivalent carbon emission factors set out the ZCH report (see Figure ii) All emissions from unregulated electricity (cooking, appliances, consumer electronics, etc.) have been discounted from the calculation. Key modelling steps followed in order to arrive at main calculations included in Appendix. See Appendix A for SAP based calculations See Appendix B for PHPP based calculations Note: More to follow, eventual intention to include SAP and PHPP worksheets 3.5 Comparison of PHPP and SAP output with Carbon Compliance criteria One recommendation of the task group was that the Carbon Compliance standard be expresssed in terms of an absolute limit on the predicted emissions of carbon dioxide (and other greenhouse gases expressed as equivalents) per square metre of internal floor space measured as an amount in kilograms per square metre per year (kg CO2(eq) /m2/year). The basis of this change was to dispense with any confusion arising from the the over 2006 Part L figure. An example of this confusion can even be seen in the Determining the Carbon Compliance limit section of the final Zero Carbon report 5, where the carbon s are discussed. The document mentions % s on the 2006 standard, however it is not made clear as to what this actually refers. There is no mention of Part L 2006 requirements, Target Emission Rate (),or indeed of the specific notional buildings which has been used for the calculation. It is acknowledged that the intention here is to steer away from s, rather than to dwell on existing methods, yet as the current SAP metric is to first derive a, this seems a strange omission. For the purposes of this report a simple calculation has be used to derive the assumed (see Figure v below). The results of this exercise appear to show that a single equivalent has been used for all three building typologies, although this may of course be coincidental. Compliance criterion Detached houses Attached houses Low rise apartment blocks Carbon emissions for house type 10 kg CO 2(eq) /m2a 11 kg CO 2(eq) /m2a 14 kg CO 2(eq) /m 2 a Equiv. over 2006 Part L 60% 56% 44% Assumed calculated from above figures Figure vii: 60% over = 10 kg CO 2(eq) /m 2 a 56% over = 11 kg CO 2(eq) /m 2 a 25 kg CO 2(eq) /m 2 a = 44% over = 14 kg CO 2(eq) /m 2 a In addition to this assumed value, a separate has been calculated for each of the projects as part of the Standard Assessment Procedure. More to follow...currents 5 Zero Carbon Hub (2011) Carbon Compliance: Setting an appropriate limit for zero carbon new homes, Technical Modelling Assumptions. Accessed May 2011 at

6 4.0 Results...notes to be populated and expanded DER output 4.2 Regional Variation To test implication of regional weather data. Reference to BRE data download page Global radiation and temperature values can be very site specific, as a result the PHPP outputs can differ for sites which have extreme exposures such as very dense urban, highly exposed or height above sea level compared to the default data sets for the region. This could affect the heating and cooling load results significantly. 6 5 Zero Carbon Hub (2011) National or Regional Weather: Implications for Carbon Compliance. Accessed June 2011 at 6 Building Research Establishment (2011) Regional Climate Data Map. Accessed June 2011 at climate data

7 4.3. Creation of a 2006 Part L equivalent building in PHPP The outputs in steps 4.1 and 4.2 show a clear range of s of PHPP outputs of 44 50% even taking into account regional differences. However whilst the figures for C0 2 /m 2 a remain absolute, the 2006 Part L base figure (from which the s are calculated) was established using SAP. The following exercise aims to calculate an equivalent building in PHPP, and compare all PHPP results to this figure. See Appendix B for full workings 5.0 Analysis, 6.0 Conclusion...to be populated......initial findings and recommendations (to be expanded) DER results between SAP, PHPP and ZCH report are surprisingly similar, suggesting that from this limited data set the ZCH modelling of the detached SPEC D PH equivalent dwelling was indeed a good representation of a Passivhaus. Regional variation ie the same building placed in different weather data produces significant enough an effect on the overall C02/space heat demand for the report to recommend regional variation being accounted for within the Carbon Compliance calculation. The amount of confusion generated from the research and discussion of s over figures was such that any future work by bere:architects is unlikely to refer to them. The report will show examples to support the ZCH recommendation for the adoption of absolute figures in place of relative s. Calls will be made for this to be incorporated as early as possible the earliest date realistically being the 2013 Part L review. Comparing space heating demand kwh/m 2 a figures and DER kg CO 2 /m 2 on the same graph has allowed for simpler correlations to be drawn between results than if two separate graphs were used.

8 Regardless of scenario/ modelling protocol, the Certified Passivhaus dwellings typically range have between 11 and 14kg CO 2 /m 2. Although the report does not intend to express a stance on the use of LZC technology, it will be acknowledged It is of key importance that the Government adopts the ZCH recommendation for built performance targets as opposed to as designed targets. Although the creation of a 2006 Part L equivalent building in PHPP may be considered by some as comparing Apples with Pears it is felt that the exercise highlights the potential underestimation of regulated emissions for past and current building regulations standard construction. Appendix A SAP Calculations Calculations for Figure iv Input data from Page 50 of ZCH Defining a Fabric Energy Efficiency Standard for zero carbon homes, Appendix A Work Group 1 Form and Fabric (2009). Carbon intensity factors from ZCH as per Figure ii Baseline Page 50 Detached house form fabric final Space heating 61.5 x Pumps & fans 1.5 x Lighting 6.5 x Total 88.6 SPEC A (NV) Page 50 Detached house form fabric final Space heating 49.7 x Pumps & fans 1.5 x Lighting 3.8 x Total 74.1 SPEC B (NV) Page 50 Detached house form fabric final Space heating 40.7 x Pumps & fans 1.5 x Lighting 3.8 x Total 65.1 DER If = % DER If = % DER If = % SPEC B (MVHR) Page 50 Detached house form fabric final Space heating 30.5 x

9 Pumps & fans 5.8 x Lighting 3.8 x Total 59.2 DER If = % SPEC C (NV) Page 50 Detached house form fabric final Space heating 30.2 x Pumps & fans 1.5 x Lighting 3.8 x Total 54.6 Spec C (MVHR) Page 50 Detached house form fabric final Space heating 15.8 x Pumps & fans 5.8 x Lighting 3.9 x Total 44.6 Spec D (MVHR) Page 50 Detached house form fabric final Space heating 7.2 x Pumps & fans 5.4 x Lighting 3.9 x Total 35.6 DER If = % DER If = % DER If = % Calculations for SAP DER outputs adjusted to take into account Carbon emissions factors Input data from Brooks Devlin, SAP worksheets to follow Carbon emission factors from ZCH as per Figure ii SAP 3 Bed Larch house Area 99 SAP 3 Bed Larch house As prepared by Brooks Devlin Space heat x water heat x pump fan etc x x x x

10 lighti ng x SAP 2 Bed Lime house As prepared by Brooks Devlin DER x DER Area SAP 2 Bed Lime house Space heat x x water heat x x pump fan etc 335 x x lighti ng x x DER = = SAP Camden Passivhaus Area As prepared by Brooks Devlin Space heat x water heat x pump fan etc x lighti ng x DER = DER = SAP Camden Passivhaus = x x x x DER = percentag e improvem ent is... If % If is (Y1 1) 41.0% percentag e improvem ent If % If is (Y1 1) 33.9% percentag e improvem ent is... If %

11 Appendix B PHPP Calculations = = If is (Y1 42.0% Calculations to removing unregulated emissions from all PHPP worksheets and to insert ZCH carbon emissions factors Worksheet Cell Range Description Adjustment Units Notes Solar DHW F11:F18 Selection of collector for solar DHW Electricity Aux Electricity F27,F33 D11:F21, D24:F25 F30 Secondary Calculation of Storage Losses Usage for cooking, electronics, appliances etc (Binary Selection) Electricity for solar DHW pump (Binary Selection) PE Value F107 Planned Annual Electricity Generation (Solar PV) Data E6 Natural gas, C0 2 equivalent emission factor E10 Electricity mix, C0 2 equivalent emission factor PHPP and SAP outputs for main calculations Values cleared N/A Removal of solar thermal collectors to demonstrate performance of fabric without addition of LZC technology Values cleared N/A No solar collectors storage losses related to solar storage tank no longer relevant Values changed to 0 Value changed to 0 N/A N/A Note: All lighting left unchanged (Row 23) as the lighting detailed on these projects is fixed and therefore part of regulated emissions Electricity use for solar DHW pump no longer relevant Value cleared kwh PV array removed for clarity (calculation is actually separate, meaning this step is not strictly necessary) Value changed to Value changed to kg/kw h Final kg/kw h Final Emission factor adjusted to align with ZCH calculation, as per ZCH 'Modelling_2016_ using_sap_2009_technical_guide' Emission factor adjusted to align with ZCH calculation, as per ZCH 'Modelling_2016_ using_sap_2009_technical_guide' Larch House Lime House Camden Passivhaus Carbon compliance result using results from PHPP (Target for Zero Carbon Compliance 10kg C0 2 /m 2 ) 14.0 kg C0 2 /m 2 a 13.5 kg C0 2 /m 2 a 12.7 kg C0 2 /m 2 a Equivalent % over of 25 kg C0 2(eq) /m 2 a (Target 60%) 44% 46% 49% Carbon compliance using results from SAP (Target for Zero Carbon Compliance 10kg C0 2 /m 2 ) 11.4 kg C0 2 /m 2 a 13.6 kg C0 2 /m 2 a 10.9 kg C0 2 /m 2 a Equivalent % using of 25 kg C0 2(eq) /m 2 a (Target 60%) 54% 46% 56% Equivalent % over individually calculated for each project (as per SAP convention) of C02(eq)/m2a of C02(eq)/m2a of C02(eq)/m2a

12 41% 34% 42% Regional Variation Larch House Lime House Camden Passivhaus Decrease of 1.0 kg C0 2 /m 2 a in Manchester weather data Carbon compliance result using average climate (East Pennines) Target for detached house 10kg C0 2 /m 2 Calculations to create a PHPP 2006 equivalent for the 3 bed Larch house Achieved by modelling to 2006 Part L fabric regulations, planned extension exercise to model an equivalent 2006 as per Notional building specifications. Certified Larch house Element 13.0kg C0 2 /m 2 a 12.6kg C0 2 /m 2 a 13.0kg C0 2 /m 2 a Equivalent over 2006 Part L Target for detached house 60% 48% 50% 48% Larch House Lime House Camden Passivhaus Decrease of 1.2 kg C0 2 /m 2 a in East Pennines weather data Build up of thermal envelope from interior to exterior. Decrease of 0.9 kg C0 2 /m 2 a in Manchester weather data Carbon compliance result using average climate (East Pennines) Target for detached house 10kg C0 2 /m kg C0 2 /m 2 a 12.5kg C0 2 /m 2 a 12.8kg C0 2 /m 2 a Equivalent over 2006 Part L Target for detached house 60% 49% 50% 49% Thickn ess (mm) U value W/(m2k) Reductions to create Part L 2006 equivalent Build up of thermal envelope from interior to exterior. Increase of 0.1 kg C0 2 /m 2 a in Manchester weather data Decrease of 1.0 kg C0 2 /m 2 a in East Pennines weather data Increase of 0.1 kg C0 2 /m 2 a in East Pennines weather data Reduced build up (mm) Floor slab Flooring 20 Flooring 20 Screed 75 Screed 75 Concrete Concrete 225 Floormate 500 A 480 Floormate 500 A 80 Total 800 Total 400 Exterior Plasterboard 15 Plasterboard 15 Walls Timber studs wood fibre ins. 100 Air gap OSB 18 Timber studs w/ frame ins. 225 Timber studs w/ frame ins. 104 Resulting U value W/(m 2 K)

13 Panelvent 9 OSB 18 Wood fibre insulation 100 Total 467 Total 162 Roof OSB 18 OSB 18 Timber truss w/ frame ins Timber truss w/ frame ins. 185 Total 578 Total 203 Exterior wall behind kitchen unit Plasterboard 15 Plasterboard 15 Softwood panel 20 Timber studs w/ fibre ins. 75 Air gap 25 OSB Timber studs w/ frame ins. 225 Timber studs w/ frame ins. 104 OSB 15 OSB 18 Wood fibre insulation 100 Total 468 Total Thermal envelope Window U values Window shading LZC technology Airtightness Space heating demand C0 2 emissions factors 2 Thermal envelope after m fabric reductions (as above) m W/(m 2 K) Window U values 2.2 W/(m 2 K) Window reveal depth ranging from m Window shading Reveal depths reduced by 0.2m 4.7 kwp PV array, flat panel solar thermal collector LZC technology Removed from calculation q 50 Air permeability 0.24m 3 /(hm 2 ) 13 kwh/m 2 a Natural gas 0.25 n 50 Air changes 0.23 h 1 Airtightness q 50 Permeability 10m 3 /(hm 2 ) Electricity Mix 0.68 Resulting space heating demand C0 2 emissions factors 155 kwh/m 2 a Natural gas n 50 Air changes h 1 Electricity Mix Ventilation MVHR, Passivhaus certified, 85% efficiency Ventilation Extract only no heat recovery